福建中立恒自动化设备有限公司
目前,世界上有200多个厂家生产可编程序控制器产品,厂家有德国的西门子,美国的Rockwell(AB)、通用(GE),日本的三菱、欧姆龙,法国的施耐德等。
可编程序控制器总的发展趋势是向高集成度、小体积、大容量、高速度、易使用、高性能方向发展。具体表现在以下几个方面:
(1)向小型化、专用化、低成本方向发展
20世纪80年代初,小型PLC在价格上还高于小系统用的继电器控制装置。随着微电子技术的发展,新型器件大幅度的提高功能和降低价格,使PLC结构更为紧凑,功能不断增加,将原来大、中型PLC才有的功能移植到小型PLC上,如模拟量处理、数据通讯和复杂的功能指令等,但价格不断下降,真正成为继电器控制系统的替代产品。
(2)向大容量,高速度方向发展
大型PLC采用多微处理器系统,有的采用32位微处理器,可同时进行多任务操作,处理速度提高,特别是增强了过程控制和数据处理的功能。另外,存储容量大大增加。
(3)与计算机联系密切
从功能上看,PLC不仅能完成逻辑运算,且计算机的复杂运算功能在PLC中也进一步得到利用,从结构上看,计算机的硬件和技术越来越多地应用到PLC;从语言上看,PLC己不再是单纯用梯形图语言,而且可用多种语言编程,如类似计算机汇编语言的语句表,甚至可直接由计算机语言编程;在通讯方面,PLC与计算机可直接相连并进行信息传递。
(4)发展多样化
可编程序控制器发展的多样化体现在3个方面:产品类型、编程语言和应用领域。
(5)模块化
PLC的扩展模块发展迅速。功能明确化、专用化的复杂功能由专门模块来完成。主机仅仅通过通讯设备向模块发布命令和测试状态,这使得PLC的系统功能进一步增强,控制系统设计进一步简化。
(6)网络与通讯能力增强
计算机与PLC之间以及各个PLC之间的联网和通讯的能力不断增强,使用工业网络可以有效地节省资源、降低成本、提高系统可靠性和灵活性,致使网络的应用有普遍化的趋势。
(7)多样化与标准化
生产PLC产品的各厂家都在大力度地开发自己的新产品,以求占据市场的更大份额。因此产品向多样化方向发展,出现了欧、美、日多种流派。与此同时,为了推动技术标准化的进程。一些国际性组织,如国际电工委员会(IEC)不断为PLC的发展制定一些新的标准,如对各种类型的产品作一定的归纳或定义,或对PLC未来的发展制定一种方向或框架。
(8)工业软件发展迅速
与可编程序控制器硬件技术的发展相适应,工业软件的发展非常迅速,它使系统应用更加简单易行,大大方便了PLC系统的开发人员和操作使用人员。
可编程序控制器的输出信号类型可以是开关量、模拟量和数字量。输出单元从广义上分包含两部分:一是与被控设备相连接的接口电路,另一部分是输出的映像寄存器。
PLC运行时CPU从输入映像寄存器读取输入信息并进行处理,将处理结果放到输出映像寄存器。输出映像寄存器由输出点相对应的触发器组成,输出接口电路将其由弱电控制信号转换成现场需要的强电信号输出,以驱动电磁阀、接触器、指示灯等被控设备的执行元件。
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